Wafer scribing method and wafer scribing device

ABSTRACT

The present invention relates to a scribing method for wafers ( 11 ), wherein a defined beam ( 12 ) is directed onto the wafer ( 11 ) by means of a beam generator means ( 10 ) so as to remove some wafer material from a wafer region. The invention also relates to a wafer-scribing device including a wafer mount ( 31 ) and a beam generator means ( 10 ) by means of which at least one defined beam can be directed onto the wafer ( 11 ).  
     The inventive method is distinguished by the by the further step of generating a first radiation pulse having a predeterminable energy density and used to create a comparatively deep pit ( 18 ) in the wafer ( 11 ).  
     The inventive wafer scribing means is distinguished by the provision that a radiation pulse can be generated by means of which a comparatively deep pit ( 18 ) can be created in the wafer ( 11 ).

FIELD OF THE INVENTION

[0001] The present invention generally relates to the scribing of wafersand more particularly to a wafer scribing method wherein a defined beamis directed onto the wafer by means of a beam generator means so as toremove some wafer material from a wafer region, and to a wafer scribingdevice including a wafer mount and a beam generator means by means ofwhich at least one defined beam can be directed onto the wafer.

BACKGROUND OF THE INVENTION

[0002] Nowadays the face of wafers is scribed in the manner of some kindof soft mark at a very low depth. Such scribing serves to recognizewafers in the process flow in the manufacture of semiconductor devicessuch as processors in particular. The reason for using soft marks of avery low depth resides in the fact that a smooth transition between thewafer plane and the pit in the wafer is required in order to achieve aconstant resist film layer at the scribing site, too. Whenever this isnot the case the reliability of the resist film layer is insufficient,which leads to the result that particles of the material may be releasedin the subsequent steps of wafer processing and might thus cause troublein the semiconductor devices. However, the inscribed flat pit is toosuperficial to survive all the operating steps throughout themanufacture of the devices. For this reason a re-inscription isnecessary. Such a re-inscription is firstly a time-consuming operationand secondly it results in impurities in possible devices because somematerial may be transferred from the scribing region to the deviceregion.

[0003] It is for this reason that the present invention seeks to providea wafer scribing method and a wafer-scribing device which avoid anycontamination and the formation of conceivable materials such as metaloxides which could dramatically interfere with or destroy thefunctionality of devices.

[0004] This problem is solved by a wafer scribing method wherein adefined beam is directed onto the wafer by means of a beam generatormeans, so as to remove some wafer material from a region of the wafer,which method provides the further operating step of generating a firstradiation pulse having a predeterminable energy density and used tocreate a deep pit in the wafer, whereas the pit is deep enough to remaina pit throughout a manufacture of semiconductor devices on said wafer.

[0005] The problem is further solved by a wafer scribing method whereina defined beam is directed onto the wafer by means of a beam generatormeans, so as to remove some wafer material from a region of the wafer,which method provides the further operating step of generating a firstradiation beam having a predeterminable energy density and used tocreate a deep pit in the wafer, whereas the pit is deep enough to remaina pit throughout a manufacture of semiconductor devices on said wafer,and whereas an edge of the pit is smooth.

[0006] The problem is moreover solved by means of a wafer scribingdevice including a wafer mount and a beam generator means, which servesto render at least one defined beam visible on the wafer, wherein aradiation pulse can be generated by means of which a comparatively deeppit can be created in the wafer, whereas the pit is deep enough toremain a pit throughout a manufacture of semiconductor devices on saidwafer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The invention will now be described in the following without anyrestriction of the general inventive idea by exemplary embodiments withreference to the drawings which are referred to expressis verbis as faras the disclosure of all the inventive details is concerned which arenot described in more details in the text. In the drawing:

[0008]FIG. 1a is a schematic representation of the operation of creatinga deep pit in a silicon wafer;

[0009]FIG. 1b is a schematic representation like that of FIG. 1a, afterthe creation of a deep pit;

[0010]FIG. 1c is an enlarged view of a detail of the wafer provided witha pit and a resist;

[0011]FIG. 2a is a s schematic illustration showing the post-processingof the pit;

[0012]FIG. 2b shows the wafer with a pit from FIG. 2a, provided with aresist;

[0013]FIG. 3a is a cross-section taken through a wafer including 6 pitsand corresponding contamination on the wafer surface;

[0014]FIG. 3b is a cross-section taken through a silicon wafer, in whichan improvement of the invention is illustrated;

[0015]FIG. 3c shows a cross-section taken through a silicon waferincluding a sacrificial film applied thereon;

[0016]FIG. 4 shows a schematic diagram of a part of a wafer scribingdevice according to an embodiment of the invention;

[0017]FIG. 5 is a schematic diagram of a preferred method according tothe invention;

[0018]FIG. 6 is a schematic diagram of another preferred methodaccording to the invention; and

[0019]FIG. 7 is a schematic diagram of still another preferred methodaccording to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] The schematic in FIG. 1a illustrates a method of scribing wafers11, wherein a beam generator means 10 is employed to direct a definedbeam 12 onto the wafer 11 for removal of some wafer material from aregion on the wafer 11, wherein moreover the further step of generatinga first radiation pulse having a predeterminable energy density isprovided which serves to create a comparatively deep pit 18 in the wafer11, i.e. a pit 18 that is deep enough to remain a pit throughoutsubsequent manufacturing steps of the wafer 11. Such a pit 18 remainsafter applying an additional layer upon the wafer. The term “pit” mayalso be understood to denote a dent or cavity or hole in particularwithin the scope of the present invention.

[0021]FIG. 1b illustrates the wafer 11 with the comparatively deep pit18 created therein. Due to the inventive process flow it is no longernecessary to perform a so-called re-inscription step so that any lumpsof material will substantially not interfere or even lead to destructionin the ongoing production of devices and specifically semiconductordevices. The re-inscription step is highly problematic already for thereason that metals or oxides, respectively, may be spattered over thewafer in particular during this re-inscription step.

[0022] Preferably a local plasma is generated for creating thecomparatively deep pit, which avoids substantially that some material 13may be spattered onto the remaining wafer portions. Whenever a laser ispreferably employed as beam generator means 10 a particularly simplescribing or pit creation is possible. Within the general scope of thepresent invention it is also possible to use a beam generator meansemitting an ionized ration or electron beams, instead of a laser.

[0023] The material 13 removed from the wafer 11 is preferablyexhausted. This is preferably achieved by the provision that the processis performed in vacuum or by means of an exhauster device which exhaustsin the vicinity of the scribing region.

[0024] The inscription is preferably produced on the edge of the waferor on the rear side of the wafer. As a result of this provision only asmall amount of remaining material or spattering material, respectively,is splashed onto the devices. When a gas jet 23 carries the materialremoved from the wafer 11 away from the wafer 11, preferably at leastduring the process of creating the comparatively deep pit 18, one canavoid any contamination of the wafer with a very high efficiency. Withthis provision the material is prevented from depositing on the wafer inparticular. The gas jet preferably flows in a direction towards thewafer edge. Moreover, the gas jet comprises preferably an inert gas. Thegas jet is preferably an N₂ jet.

[0025] When preferably a sacrificial layer 24 is applied on the wafer 11before the comparatively deep pit 18 is created in the wafer 11, andwhen preferably the sacrificial layer is subsequently removed there isalso an efficient possibility available to keep any contaminatingmaterial away from the wafer. The sacrificial layer is preferablyremoved by a further etching step. The sacrificial layer may preferablybe an organic layer or an oxide layer. This layer collects thecontaminant or slag, for instance, such as SiO_(X), thus permitting theremoval thereof by removing the sacrificial layer from semiconductordevices prior to the steps of the manufacturing operation. Acorresponding sectional view of a wafer with a sacrificial layer 24applied thereon is illustrated in FIG. 3c.

[0026] Any possibly existing residual contaminants 19 and 20, whichremain on the wafer 11 as a result of the creation of the comparativelydeep pit 18 in the wafer 11 are preferably reduced or removed by asubsequent evaporation step using a second radiation pulse. In thisoperation the energy density of the second radiation pulse or theparameters of this radiation pulse such as power, energy of the lightquanta impinging on the contaminant, etc., are preferably matched sothat substantially only the contaminant will be evaporated exclusively.

[0027] Moreover, a further radiation pulse is generated as a furtherstep of operation, which, compared against the first radiation pulse,presents a lower energy density and causes the wafer material tocommence fusing. Due to this preferred embodiment of the method it ispossible to produce very smooth edges between the wafer surface and thepit 18. This is schematically illustrated specifically in FIGS. 2a and 2b. The fused wafer material 14 is represented by undulated arrows.

[0028] It is furthermore preferred that a plurality of mutually spacedcomparatively deep pits 18 should be created. Moreover, a pit ispreferably created by the first radiation pulse and the pit so producedis subjected to the action of the further radiation pulse prior to thecreation of another pit 18. In this manner a pit is produced whichpresents a smooth transition or smooth edge 17, respectively, to theother corresponding pit.

[0029] It is preferred that initially all pits are created by the firstradiation pulses and that only thereafter all pits are subjected to theaction of the further radiation pulses. In this manner it is notnecessary to generate two different radiation pulses of different energydensities in alternation; instead initially the scribing is performedwith appropriate mimics with deep pits which present comparatively sharpedges 16 whereupon these pits are then converted into pits with smoothedges 17 by means of the respective further radiation pulses.

[0030] The depth of the pit preferably amounts to 3 μm to 10 μm. Thedepth of the pit is preferably within the range between 4 μm and 6 μm.

[0031] The problem of the invention is furthermore solved by a waferscribing device including a wafer mount 31 and a beam generator means 10which is used to direct at least one defined beam 12 onto the wafer 11especially in a wafer region 9 whilst it is possible to generate aradiation pulse by means of which a comparatively deep pit 18 can becreated in the wafer 11.

[0032] One exemplary embodiment of such a wafer-scribing device isschematically illustrated in FIG. 4. This inventive wafer-scribingdevice presents the advantage that this device can be used to achieve aninscription on wafers in a comparatively simple manner, without anycontaminants such as slag in particular depositing on the wafer or withonly very slight quantities thereof collecting on the wafer.

[0033] Preferably at least one optical element 32 is provided which maybe used to focus the radiation pulse. With such focusing it is possiblein a simple manner to adjust the energy densities on the wafer surface.The optical element 32 is preferably supported for displacement alongthe laser beam direction. The beam power emerging from the beamgenerator means is preferably adjustable so that the energy density orthe power density at the wafer site is adjustable, too, which isparticularly preferred.

[0034] It is furthermore preferably that the beam generator means 10emits radiation pulses of different power, particularly in alternation,at short intervals. With this provision it is easily and simply possibleto create first a pit having a comparatively sharp edge 16, whereuponthis sharp edge is rendered smooth. To this end the beam generator means10 comprises at least two beam generator means emitting radiation pulsesof different power levels. This embodiment is schematically illustratedin FIG. 4 in particular. It is furthermore preferred that the beamgenerator means also includes at least one beam deflector unit 30.

[0035] The beam generator means 10 comprises preferably at least onelaser. The laser is preferably a YAG laser operating preferably at awave length of 1,064 nm in particular and having a power level of <1 W.It is particularly preferred that the laser generates a laser pulse at apower level of 0.8 W.

[0036] It is moreover preferred that one part of the radiation pulse canbe masked out. When a central, specifically circular, fraction of theradiation pulse can be masked out by means of an aperture, which isparticularly preferred, it is possible to render only the edge area, i.e. the area of the edge of the pit, smooth selectively.

[0037] An installation for the manufacture of semiconductor devices,particularly semiconductor processors, is preferably equipped with awafer-scribing device of the aforedescribed type.

[0038] The process flow illustrated in FIGS. 1a, 1 b and 1 c furnishescomparatively thin resist thicknesses at the sharp edge 16 of the pit18. The resist layer is identified by the reference numeral. In someprocess flows it is possible that the resist 15 breaks up at the sharpedge 16 as a result of the creation of deep trenches. Such breaking-upof the resist 15 during the manufacture of deep trenches is caused byblack silicon or corresponding needles, respectively.

[0039] In such a case it is advisable to convert the sharp edge 16 intoa smooth edge 17, which is realized by means of a second laser pulsehaving a lower energy density, as is illustrated in FIG. 2a. With thisprovision a smooth transition is achieved between the pit edge and thewafer plane. To this end laser light is preferably used which isradiated substantially only onto the edge. As a matter of fact, FIG. 2ashows a laser beam which renders the pit 18 smooth over the entire area.It is possible instead, as has been set out above, to employ also somekind of laser light ring. Since as a result of edge smoothing or edgerounding a re-inscription is not necessary costs are saved on account ofthe shorter process flow.

[0040]FIG. 2b shows a corresponding sectional view of a wafer 11including a deep pit 18 which has already been smoothed or rounded offby the previous step so that a soft edge 17 is shown. A resist 15 isapplied on the wafer

[0041] For the creation of the deep pit the laser is preferably so setthat no slag will collect on the wafer, as is shown in FIG. 3a. FIG. 3ais a sectional view of a wafer 11 in which pits 18 are created by meansof a laser, with the pits 18 having been created, as a matter of fact,at a comparatively high energy density so that slag or othercontaminations from the area of the respective pits will collect on thewafer surface. Here a distinction is made between ejecta slag 19 andcrater slag 20. When an optical character recognition (OCR) system isemployed the wafer scribing method is preferably so modified thatsmaller and flatter pits or recesses, respectively, are produced whicheven though they are invisible to the eye they are yet recognizable bythe OCR system.

[0042] Moreover, the scribing marking is preferably performed on theextreme wafer edge, preferably between the edge exclusion zone and theedge which is comparatively far away from the region of the activedevices. The marking site is, of course, dependent on the mask layout.

[0043] The prevention of the creation of the aforementioned defects,i.e. any material or slag possibly collecting in the active region ofthe devices, results in the advantage that any further cleaningoperations are not required after laser scribing. Such cleaning agentsare aggressive and might cause damage to or roughen the silicon surface,which may be detrimental to the yield in terms of devices. As suchmaterial defects or material depots do not occur with the inventivemethod such cleaning operations may be avoided, which leads to a shorteroperating period and to reduced costs of materials.

[0044] The aforedescribed inventive and preferred method is employedparticularly preferably for devices produced by a lithographic method,which presents structures of less than 0.18 μm. This is the case with300 mm wafers in particular.

[0045] Moreover, defects or deposits on the rear side of the wafer or amount 31 holding the wafer (or a stepper chuck) take an influence on theproduction of devices. The reason for this is the fact that the waferflatness is influenced, which is detrimental to the resolution of thelithographic structures on the wafer or the substrate, respectively. Thestepper chuck may also be contaminated by particles or materials appliedfrom the rear side of the wafer. This may result in a fault in thestructures. Such structural faults, particularly faults in opticalstructures in lithographic processes, require correction. At present sofar not any possibility has been made available to diagnose this problemat all or to remove the defects from the stepper chuck. The wafersproduced by the normal scribing methods moreover present irregularitiessuch as bubbles, bumps, and topography-related problems.

[0046] Accordingly, a preferred embodiment of the invention isillustrated in FIG. 3b. On account of the modification shown in FIG. 3bsome kind of shield is provided, with utilization of a specificallyfiltered nitrogen jet (N₂ jet) which is directed towards the wafer edgefor deflection of slag. In a preferred combination with high-performancevacuum pumps or exhauster devices the deflected slag particles orcontaminations can be efficiently removed from the surface. The N₂ gasjet is so arranged that it produce some kind of gas cushion or gas padwhich blocks the surface for slag or deflects slag towards the vacuum,respectively. The angle of the laser may be preferably so oriented thatthe slag is conveyed towards the vacuum or to the wafer edge.

[0047] A corresponding pit presents commonly a diameter of 20 mm to 100mm. The aggregated pits produce an inscription, which is usedparticularly for the identification of wafers.

[0048] The method is preferably carried out at room temperature.

[0049]FIG. 5 shows a schematic diagram of a preferred method accordingto the invention. In step 100 the laser and the wafer or the laseroptics and the wafer are aligned such that it is possible to direct adefined laser beam which is preferably focused onto the wafer surface.In the next step at 101 a first laser pulse is generated. In step 102the laser pulse is directed to the wafer surface and wafer material isejected from the wafer. The laser energy density and the length of thepulse is predeterminable and preferably such that the pit which iscreated due to the ejection of wafer material is deep enough to remain apit also during the subsequent process steps for the production ofsemiconductor devices or semiconductor elements.

[0050] Preferably the energy density is such that the wafer material isnot only ejected from the wafer but also softened or fused in such amanner that a smooth edge is produced.

[0051] In step 103 the question arises whether all pits necessary forthe scribing or the recognition of the wafer have been produced. If theanswer is yes the method ends at step 104. If the answer is no themethod again starts at 100, in which the laser and the wafer are alignedagain to produce another pit, which is located in the region of thescribing area of the wafer.

[0052] In FIG. 6 another preferred embodiment according to the presentinvention is shown. There are two further steps 105 and 106 shown, whichare performed within the method steps of FIG. 5. At 105 a second laserpulse is generated and at 106 this laser pulse is directed to the pit orthe edges of the pit to smooth the edges. In this embodiment of theinvention two laser pulses are used to produce a pit with smooth edges.Each pit is produced sub-sequently. The laser beam energy density orlaser-pulse energy density of the second laser pulse is preferably lowerthan that of the first laser pulse.

[0053]FIG. 7 shows still another preferred embodiment of the invention.In this embodiment almost all pits are produced by the first laserpulses at step 101 and 102 and checked in step 107. After all these pitsare produced, edge smoothing starts at 108. All edges of the pits aresmoothed at steps 105 and 106 and are checked in step 109.

[0054] While the invention has been described in terms of particularstructures it should be apparent that this invention is not restrictedto the embodiments which are described. The invention is not restrictedto silicon wafers but may be implemented with other semiconductors orother materials. While the principles of the invention have beendescribed here it is to be clearly understood by those skilled in theart that this description is presented only by way of example and not asa limitation to the scope of the invention. It is accordingly intendedthat the appended claims should cover all those modifications of theinvention which fall within the true spirit and the scope of theinvention.

List of reference numerals

[0055]9 wafer region

[0056]10 laser

[0057]11 silicon wafer

[0058]12 laser beam

[0059]13 evaporated silicon

[0060]14 fused silicon

[0061]15 protective layer (resist)

[0062]16 sharp edge

[0063]17 smooth edge

[0064]18 pit

[0065]19 ejecta slag

[0066]20 crater slag

[0067]21 laser scribe pits

[0068]22 gas shield

[0069]23 gas jet

[0070]24 sacrificial film

[0071]30 prism

[0072]31 mount

[0073]32 lens

[0074]32 aperture

[0075]100 align laser and wafer

[0076]101 generate first laser pulse

[0077]102 eject wafer material

[0078]103 all pits produced

[0079]104 end

[0080]105 generate second laser pulse

[0081]106 smooth edge

[0082]107 check depth

[0083]108 start edge smooth

[0084]109 check edge smooth

1. A scribing method for wafers, wherein a defined beam is directed ontosaid wafer by means of a beam generator means so as to remove some wafermaterial from a wafer region, characterized by the further step ofgenerating a first radiation pulse having a predeterminable energydensity and used to create a deep pit in said wafer, whereas the pit isdeep enough to remain a pit throughout subsequent manufacturing steps ofsaid wafer.
 2. The method according to claim 1, characterized in that alocal plasma is generated for creating said deep pit.
 3. The methodaccording to claim 1, characterized in that a laser is used as said beamgenerator means.
 4. The method according to claim 1, characterized inthat the material removed from said wafer is exhausted.
 5. The methodaccording to claim 1, characterized in that a gas jet carries thematerial removed from said wafer away from said wafer at least duringthe creation of said deep pit.
 6. The method according to claim 5,characterized in that said gas jet flows in a direction towards thewafer edge.
 7. The method according to claim 5, characterized in thatsaid gas jet comprises inert gas.
 8. The method according to claim 5,characterized in that said gas jet is a N₂ jet.
 9. The method accordingto claim 1, characterized in that a sacrificial layer is applied on saidwafer before said deep pit is created in said wafer, and that saidsacrificial layer is subsequently removed.
 10. The method according toclaim 1, characterized in that any residual contaminations possiblypresent, which remain on said wafer as a result of the creation of saiddeep pit in said wafer, are reduced or removed by a subsequentevaporating step using a second radiation pulse.
 11. The methodaccording to claim 10, characterized in that the beam parameters forremoval or reduction of said residual contaminations are matched. 12.The method according to claim 1, characterized in that a furtherradiation pulse is generated as a further step of operation, which,compared against said first radiation pulse, has a lower energy densityand causes the wafer material to commence fusing.
 13. The methodaccording to claim 1, characterized in that a plurality of mutuallyspaced deep pits is created.
 14. The method according to claim 13,characterized in that a pit is created by means of said first radiationpulse and that the pit so created is subjected to the action of saidfurther radiation pulse prior to the creation of a further pit.
 15. Themethod according to claim 13, characterized in that initially each ofsaid holes or pits is created by means of said first radiation pulse andthat only then all holes or pits are each subjected to the action ofsaid further radiation pulse.
 16. The method according to claim 1,characterized in that the depth of said pit is within the range between3 μm and 10 mm.
 17. The method according to claim 16, characterized inthat the depth of said pit is within the range between 4 μm and 6 μm.18. A wafer scribing device including a wafer mount and a beam generatormeans by means of which at least one defined beam can be directed ontosaid wafer, characterized in that a radiation pulse can be generated bymeans of which a deep pit can be created in said wafer, whereas the pitis deep enough to remain a pit throughout subsequent manufacturing stepsof said wafer.
 19. The wafer scribing device according to claim 18,characterized in that at least one optical element is provided by meansof which it is possible to focus said radiation pulse, with said opticalelement being disposed for displacement along the direction ofpropagation of said radiation pulse in particular.
 20. The waferscribing device according to claim 18, characterized in that theradiation energy emerging from said beam generator means is adjustable.21. The wafer scribing device according to claim 18, characterized inthat said beam generator means emits radiation pulses of different powerlevels at short intervals, particularly in alternation.
 22. The waferscribing device according to claim 18, characterized in that said beamgenerator means comprises at least two beam generator means emittingradiation pulses of different power.
 23. The wafer scribing deviceaccording to claim 22, characterized in that said beam generator me anscomprises moreover at least one beam deflector unit.
 24. The waferscribing device according to claim 18, characterized in that said beamgenerator means comprises at least one laser.
 25. The wafer scribingdevice according to claim 18, characterized in that one fraction of saidradiation pulse can be masked out.
 26. The wafer scribing deviceaccording to claim 25, characterized in that a central, particularlycircular, portion of said radiation pulse can be masked out by means ofan aperture.
 27. A system for manufacturing semiconductor devices,specifically semiconductor processors, including a wafer scribing deviceaccording to claim
 1. 28. A scribing method for wafers, wherein adefined beam is directed onto said wafer by means of a beam generatormeans so as to remove some wafer material from a wafer region,characterized by the further step of generating at least one of a firstradiation beam and a second radiation beam having a predeterminableenergy density and used to create a deep pit in said wafer, whereas thepit is deep enough to remain a pit throughout subsequent manufacturingsteps of said wafer and whereas the edge of the pit is smooth.
 29. Themethod of claim 28, characterized in that said second radiation beamsmoothes the edge of the pit.
 30. The method of claim 28, characterizedin that the first and/or the second radiation beam is at least a pulse.